Modality-Independent Core Brain Network for Language as Proved by Sign Language

The human brain has the capacity to automatically compute the grammatical relations ofwords in sentences, be they spoken or written. This species-specific ability for syntax lies atthe core of our capacity for language and is primarily subserved by a left-hemispheric fronto-temporal network consisting of the posterior inferior frontal gyrus (pIFG), as well as theposterior middle temporal gyrus and superior temporal sulcus (pMTG/STS). To date, itremains unclear whether this core network for syntactic processing identified for spoken andwritten language in hearing people also holds for the processing of the grammatical structureof a natural sign language in deaf people. Using functional magnetic resonance imaging, asign language paradigm that systematically varied the presence of syntactic and lexical-semantic information, and meta-analytically defined functional regions-of-interests derivedfrom a large dataset of syntactic processing in hearing non-signers, we demonstrate that deafnative signers of German Sign Language (DGS) also recruit left pIFG and pMTG/STS forcomputing grammatical relations in sign language—indicating the universality of the corelanguage network. These findings suggest that the human brain evolved a dedicated neuralnetwork for processing the grammatical structure of natural languages independent oflanguage modality, which flexibly interacts with different externalization systems dependingon the modality of language use.